Drilling glass looks intimidating, but with the right tool it is straightforward and clean. The best drill bits for glass are diamond-coated, because glass is a hard, brittle material that ordinary twist bits simply cannot cut without cracking or shattering the pane.
What to Look For
Glass has no grain and does not shave away like wood or shear like metal — it must be abraded. That means you need an abrasive bit, steady water cooling and low speed. A conventional pointed twist drill concentrates force on a tiny spot and stresses the surface until it fractures. Instead, look for a bit that grinds rather than gouges, and always support the glass on a flat, cushioned surface so it cannot flex. The three factors that decide success are the abrasive on the tip, the heat you remove and the pressure you apply.
The Best Type of Bit for Glass
Diamond drill bits are the clear choice. Industrial diamond grit is bonded to the tip, and because diamond is harder than glass it wears the surface away gradually and predictably. Both hollow core-style and rounded-tip diamond bits work well; the key difference is that core bits cut only a ring and run cooler on larger holes, while solid tips suit small pilot holes.
- Material: diamond-coated bits abrade glass, tile, porcelain and ceramic without cracking them.
- Speed: run slow, roughly 400–900 RPM, to keep the tip cool and the cut controlled.
- Cooling: keep water on the tip constantly — a dam of putty holding a small pool works well.
- Pressure: use very light pressure and let the grit do the work; forcing the bit invites breakage.
Technique That Prevents Cracks
Start the bit at a shallow angle to establish a small groove, then bring it upright so it does not skate across the slick surface. A square of tape over the mark also helps the tip bite without wandering. Keep the water flowing the whole time; if you see the tip drying or smoking, stop and cool it. Ease off almost completely as you approach the far side, where the majority of cracks happen when the bit breaks through. Never use hammer or impact modes with glass, and never rush. American-made diamond bits hold their grit longer, giving you more clean holes per bit before the tip wears smooth.
Matching the Bit to the Job
Small diamond bits suit bottles, mirrors, sea glass and craft projects, while larger core diameters suit ceramic tile and stone. Tempered glass cannot be drilled at all — only annealed glass, so check before you start because a tempered pane will simply explode. Position your hole well away from any edge, since glass is weakest there and prone to running a crack outward. If you are unsure how abrasive and coated bits differ from standard steel bits, our reference guides break down which bit fits which material so you can order once and drill with confidence rather than guessing at the counter.